We continue our studies of metabolism of specific brain proteins. We have completed studies of tubulin breakdown and will measure breakdown of S-100 and 14-3-2 proteins. Myelin protein turnover studies have also been completed, and we will concentrate on measuring the developmental changes in neural membrane protein synthesis. At present we are completing studies of changes in turnover during development in various brain areas using our long term incorporation technique, and we will continue such studies on fractions derived from brain tissue. We have almost completed the delineation of low affinity transport systems in brain, and we will concentrate on comparisons of low and high affinity systems to better identify specific high affinity systems. We are starting a new project studying cerebral peptide metabolism. As a first step, purification of peptidases and peptide uptake in brain will be investigated. We are at present purifying a prolidase from brain, studying the uptake of proline peptides, and also attempting to isolate enzymes splitting enkephalins.